(i) Field of the Invention
The present invention relates to a sealing device for a rotary fluid machine capable of realizing a high-speed safe drive by utilizing an oil fed to the sealing device, introducing an assembly having an additional bearing function into the sealing device, and pressing the assembly downward by the force of hydraulic pressure in order to increase the number of kinetic fulcrums from 2 in the case of a conventional bearings to 4 and to thereby heighten a safe speed of the shaft.
(ii) Description of the Prior Art
The outline of a conventional sealing device will be described in reference to FIGS. 6 and 7.
The conventional rotary fluid machine such as a compressor, an air blower and a turbine has two bearings disposed opposite end portions in a shaft chamber, and in the case of the rotary fluid machine in which a rotary shaft is provided extending through the shaft chamber, it has intensively been required to drive a long thin rotary shaft at a high speed with the intention of improving a hydrodynamic efficiency.
However, when the long thin rotary shaft is supported by the opposite bearings alone and its driving is carried out, a safe speed of the shaft will deteriorate. If the rotary shaft is driven at a higher rotational frequency than the safe speed, an uncontrollable turning force will be generated by a fluid running in the shaft chamber and will bring about an unstable vibration in a rotary shaft system. This vibration will diffuse with time, so that a sealing state provided between the shaft chamber and the shaft will be damaged and an excessively strong contact will take place between rotary bodies and stationary portions and will break them. After all, the operation of the rotary fluid machine will be made impossible.
In order to prevent such an unwelcome phenomenon, i.e., in order to heighten the safe speed of the usual shaft, the latter has been thickened at the sacrifice of the hydrodynamic performance, and/or the number of the shaft chambers has been increased.
FIG. 6 is a sectional view illustrating a conventional centrifugal compressor entirely. Reference numeral 1 is a shaft chamber, numeral 2 is a rotary shaft, 3 is each of bearings disposed at the opposite end portions in the shaft chamber 1, and 4 is each seal.
In such a conventional sealing device as shown in FIG. 7, an atmospheric side seal ring 6 and an in-chamber side seal ring 7 are disposed in a housing 5, with these rings 6, 7 separated from the shaft 2 via a small space. This constitution prevents a high-pressure oil fed between both the seal rings 6, 7 from leaking out. Both the seal rings 6, 7 are adapted to freely slide on inner surfaces of the housing 5 which are perpendicular to an axis of the shaft 2, in compliance with the whirling of the shaft 2. Therefore, such an oil membrane seal has no reaction force to the whirling shaft.